Desorption and plant-availability of phosphate sorbed by some important minerals

Abstract

Experiments were conducted to study the desorption characteristics and plant-availability of phosphate sorbed by some important variable-charge minerals including kaolinite, goethite and amorphous A1 oxide. Phosphate desorption from the complexes of goethite-P, kaolinite-P and A1 oxide-P by equilibration with 0.02 M KC1, resin or some commonly used chemical extractants was slow compared to desorption from a permanent-charge mineral (montmorillonite). However, rice plants were not observed under P deficiency in a pot trial with a phosphate-mineral complex as the only P source for both the permanent-charge mineral and the variable-charge minerals at either 50% or 100% sorption saturation with the exception of goethite-P at 50% saturation. In the exceptional goethite-P treatment, plant P concentration (1.0 g kg-l) was on the threshold of P deficiency. From 15% to 31% of the applied P was recovered by the plants within a growing period of three months, depending on sorption saturation and mineral type. Both the dry matter yield and P uptake decreased with decreasing sorption saturation for all the tested complexes except for A1 oxide-P100 (100% saturation). In the case of A1 oxide-P10o, A1 toxicity may have occurred, for poor root growth and high A1 concentration in the plants were observed. The effect of sorption saturation on the yield and P uptake of plant was obvious for kaolinite and goethite but not very significant for montmorillonite. Based on the recovery of applied P, the plant-availability decreased in the following order: kaolinite-P10o > goethite-P10o > A1 oxide-Ps0 > montmorillonite-Pl0o > montmorillonite-Ps0 > kaolinite-P50 > goethite-Ps0. Fractionation of the sorbed P before and after plant uptake showed that most of the P uptake originated from the resin-exchangeable P fraction in montmorillonite-P complex, but came mainly from NaOH-extractable fractions in goethite-P complex, whereas all the resin-P, NaHCO3-P and NaOH-P fractions in kaolinite-and amorphous A1 oxide-P complex made a contribution to P uptake.

Influence of soil pH on inorganic phosphorus sorption and desorption in a humid brazilian Ultisol

“…Therefore, increasing K d is interpreted as increasing the rate of change in P desorption at a particular solution P concentration, as was observed for all levels of P loading when soil pH was raised to 7.1. Similar results can be found among the limited P desorption studies previously reported (He et al, 1994;De Smet et al, 1998).…”

“…Increased pH levels to 6.0 and 7.1 caused the release of an additional 0.2 to 1.0 and 0.7 to 2.7 kg ha -1 of sorbed P into soil solution for prompt plant uptake. These results are consistent with the findings of He et al (1994). He and associates determined P desorption from a variety of minerals and ranked the minerals according to their desorption capacity: goethite < kaolinite < amorphous Al oxide < montmorillonite.…”

Microbial biomass phosphorus and its significance in predicting phosphorus availability in red soils

“…Because of strong adsorption and occlusion of phosphate by Fe and Al oxides, the utilization efficiency of applied and indigenous soil P to crops is very low (<5-15%) (Lin, 1995). Phosphorus deficiency is one of the critical soil constraints to crop production in the red soil regions (He et al, 1990(He et al, , 1994(He et al, , 1996. Development of adequate chemical and biochemical index of P availability is critical for enhancing crop production on the red soils.…”

Assessing Methods for Developing Phosphorus Desorption Isotherms from Soils using Anion Exchange Membranes

“…Anion exchange materials have been used to investigate the desorption kinetics of P (Raven and Hossner, 1994), measure P mineralization (Parfitt et al, 1994), and measure total resindesorbable P by sequential extraction (He et al, 1994). However, P desorption isotherms using AEMs have seldom been developed.…”